1. Field of the Invention
The present invention relates to a vibrator and a production method therefor, and more particularly, to a vibrator used in, for example, a piezoelectric vibrating gyroscope arranged to detect the angular velocity and a production method therefor.
2. Description of the Related Art
FIGS. 11A to 11C include cross-sectional views of known vibrators.
As shown in FIG. 11A, a vibrator 1 includes, for example, a first piezoelectric substrate 2a and a second piezoelectric substrate 2b. The first piezoelectric substrate 2a and the second piezoelectric substrate 2b are stacked with a joint layer 3 disposed therebetween. Further, the first piezoelectric substrate 2a and the second piezoelectric substrate 2b are polarized in opposite thickness directions, as shown by the arrows in FIG. 11A. Two split electrodes 4a and 4b are provided on a principal surface of the first piezoelectric substrate 2a so as to be spaced from each other in the width direction. A common electrode 5 is provided on a principal surface of the second piezoelectric substrate 2b (see Japanese Patent Application Publication No. H7-332988).
For example, the vibrator 1 is used in a piezoelectric vibrating gyroscope arranged to detect the angular velocity. A driving signal, such as a sinusoidal signal, is applied to the split electrodes 4a and 4b and the common electrode 5 in the vibrator 1. The driving signal causes the first piezoelectric substrate 2a and the second piezoelectric substrate 2b to be displaced in opposite directions. In this case, when the first piezoelectric substrate 2a expands in a direction parallel to the principal surface thereof, the second piezoelectric substrate 2b contracts in the direction parallel to the principal surface thereof. Conversely, when the first piezoelectric substrate 2a contracts in the direction parallel to the principal surface thereof, the second piezoelectric substrate 2b expands in the direction parallel to the principal surface thereof. For this reason, the first piezoelectric substrate 2a and the second piezoelectric substrate 2b bend in a direction substantially orthogonal to the principal surfaces thereof. When the vibrator 1 is rotated about a center axis O in this state, since different signals are output from the two split electrodes 4a and 4b, a signal corresponding to the angular velocity of rotation can be detected by detecting a difference between the output signals from the two split electrodes 4a and 4b. The angular rotation velocity can be determined from the output signal.
For this vibrator 1, a step of joining the two substrates is performed. The joining step reduces the production efficiency during mass production, and also causes variations in the characteristics among the vibrators. When the joint layer 3 is made of an organic adhesive, such as an epoxy adhesive, the adhesive also vibrates during excitation of the vibrator 1. Consequently, the detection efficiency of the angular velocity is reduced. Moreover, the vibration state changes with changes of the adhesive due to the temperature, and the detection sensitivity of the angular velocity varies.
Accordingly, a vibrator 6 shown in FIG. 11B is a vibrator which does not include a joint layer.
In the vibrator 6, electrodes 8a, 8b, 8c and electrodes 8d, 8e, and 8f are provided on opposite surfaces of a vibrating body 7 shaped, for example, like a quadrangular prism. The vibrating body 7 is polarized from the electrode 8e toward the electrodes 8a, 8b, and 8c, and is also polarized from the electrode 8e toward the electrodes 8d and 8f (see Japanese Patent Application Publication No. H11-83496).
A vibrator 9 shown in FIG. 11C is another vibrator which does not include a joint layer.
The vibrator 9 includes a vibrating body 10, shaped, for example, like a quadrangular prism, and two split electrodes 11a and lib are provided on one principal surface so as to extend in the longitudinal direction and to be spaced from each other in the width direction. A common electrode 12 is provided on substantially the entire principal surface of the vibrating body 10 opposite to the surface on which the split electrodes 11a and 11b are provided. The vibrating body 10 is strongly polarized toward the split electrodes 11 and 11b on a side close to the surface including the split electrodes 11a and 11b, and is weakly polarized on a side close to the common electrode 12. This is obtained by heating one side of the vibrating body 10, which has been polarized in the thickness direction beforehand, to a temperature greater than or equal to the Curie point so as to weaken the polarization, and by cooling the other side so as to maintain the polarization (Japanese Patent Application Publication No. 2000-314629).
Since the above-described vibrators 6 and 9 do not include a joint layer, the problems of the related art resulting from the joint layer are not produced.
As described above, in the joint-type vibrator 1, since the step of joining the first piezoelectric substrate 2a and the second piezoelectric substrate 2b is performed, the production efficiency during mass production is reduced.
The vibrator 6 has a problem in that the electromechanical coefficient thereof is less than that of the joint-type vibrator 1. While the unimorph vibrator 9 has an electromechanical coefficient greater than that of the vibrator 6 in which the polarizing direction of a portion is changed, only one side of the vibrating body 10 in the thickness direction is displaced by the driving signal, and therefore, the obtained electromechanical coefficient is less than or equal to half the electromechanical coefficient of the joint-type vibrator 1.
In this manner, the joint-type vibrator has a problem of reduced production efficiency, and the vibrator having no joint layer has a problem of reduced electromechanical coefficient, that is, the exchange efficiency between electrical energy and mechanical energy is low.